Intravascular ultrasound (IVUS) imaging is widely used in interventional cardiology as a diagnostic tool for assessing a diseased vessel, such as an artery, within the human body to determine the need for treatment, to guide the intervention, and/or to assess its effectiveness. An IVUS device including one or more ultrasound transducers is passed into the vessel and guided to the area to be imaged. The transducers emit ultrasonic energy in order to create an image of the vessel of interest. Ultrasonic waves are partially reflected by discontinuities arising from tissue structures (such as the various layers of the vessel wall), red blood cells, and other features of interest. Echoes from the reflected waves are received by the transducer and passed along to an IVUS imaging system. The imaging system processes the received ultrasound echoes to produce a cross-sectional image of the vessel where the device is placed.
There are two types of IVUS catheters commonly in use today: rotational and solid-state. For a typical rotational IVUS catheter, a single ultrasound transducer element is located at the tip of a flexible driveshaft that spins inside a plastic sheath inserted into the vessel of interest. The transducer element is oriented such that the ultrasound beam propagates generally perpendicular to the axis of the device. The fluid-filled sheath protects the vessel tissue from the spinning transducer and driveshaft while permitting ultrasound signals to propagate from the transducer into the tissue and back. As the driveshaft rotates, the transducer is periodically excited with a high voltage pulse to emit a short burst of ultrasound. The same transducer then listens for the returning echoes reflected from various tissue structures. The IVUS imaging system assembles a two dimensional display of the vessel cross-section from a sequence of pulse/acquisition cycles occurring during a single revolution of the transducer.
In contrast, solid-state IVUS catheters carry an ultrasound scanner assembly that includes an array of ultrasound transducers distributed around the circumference of the device connected to a set of transducer control circuits. The transducer control circuits select individual transducers or a combination of transducers for transmitting an ultrasound pulse and for receiving the echo signal. By stepping through a sequence of transmitter-receiver pairs, the solid-state IVUS system can synthesize the effect of a mechanically scanned transducer element but without moving parts. Since there is no rotating mechanical element, the transducer array can be placed in direct contact with the blood and vessel tissue with minimal risk of vessel trauma. Furthermore, because there is no rotating element, the interface is simplified. The solid-state scanner can be wired directly to the imaging system with a simple electrical cable and a standard detachable electrical connector.
IVUS imaging can be utilized before, during, and/or after a percutaneous coronary intervention (PCI). For example, IVUS imaging can be used for diagnosis and treatment planning to determine an appropriate diameter and length for a stent to be positioned within an occluded blood vessel. For example, after stent deployment, IVUS imaging can be used to determine if the stent is properly placed within the vessel. IVUS imaging can provide information about the vessel lumen and borders, whether the stent is well apposed to the vessel lumen, and other information for diagnosis and/or post-treatment assessment. While conventional IVUS systems provide border and lumen information, it is generally not accurate enough to automatically make treatment and a post-treatment assessment decisions. Thus, conventional IVUS imaging systems generally require human image interpretation to determine a proper diameter and length for the stent and whether the stent is well apposed to the vessel lumen.
Thus, there remains a need for intravascular ultrasound imaging system that provides a high accuracy model of vessel anatomy.